Color mixing is one of the most difficult aspects of painting. Back in Holbein's day it wasn't too difficult simply because there were so few colors from which to chose. Today's huge spectrum of colors makes choosing colors difficult. Should I choose a red that stays warm when mixed with white or should I choose one that becomes cool when mixed with white? The answer to the above question involves knowing the characteristics of more than two dozen red pigments - and five different whites.
Confusing? You bet. That's why skilled painters have always 'set' a palette before painting. If you are about to paint a traditional portrait there's not much likelihood that you'll need to have a bright lime green or electric blue on the palette . . . at least, not for the flesh tones. Similarly, one would set a different palette for painting a green meadow than for painting an arid arroyo.
Caucasian flesh tones are composed of yellows and reds with greys added to neutralize certain areas. Caucasian flesh tones have the widest variation within the individual face. There is wide variation in brown flesh tones, ranging from cool to warm but less variation within the individual face. What we think of as Asian flesh tones tend toward less variation than brown flesh tones and considerably less variation in tone within the individual face. The flesh tones of males of all races are usually depicted as somewhat darker and more richly colored than the flesh tones of corresponding females. Children are always depicted as having lighter flesh tones, on the order of the females of the race but with higher color in the cheeks, nose and ears.
The head can be divided into three areas: forehead, cheeks and jaw. The forehead receives light in such a way that it is generally 1/2 a Value higher in tone than the rest of the face. The blood supply is less than in the fleshy parts of the face and, as a result, the skin is more yellow in tone. The ochre and sienna mixtures can be used for the mass tone.
The ears, cheeks and nose (as well as the mouth) have an ample blood supply that makes them red. As people age that blood supply is less in evidence. Children and infants are characterized by their red cheeks. The reddish mixtures in the center of the palette are for those areas in the center of the face. They are mixed with the mass tone.
The area under the nose - the jaw, has the most neutral color. In men, that neutralized color is made prominent by the beard area. But even in women, that area has a bit less color than the other areas of the face. When painting women be very careful to avoid neutralizing that area too much or the sitter will appear to need a shave. The neutral tones of raw umber and ivory black are mixed with the mass tone.
The neck should be slightly neutralized. Visual greys made from alizarin crimson and viridian can be mixed with the masstone to produce a convincing area under the chin. Alizarin and grey can be mixed with the mass tone to render a convincing transition between the forehead and the hair.
The accompanying illustrations were done to show those tonal transitions, thus all of the transitions are more obvious than they should be. The above illustration would be a good basis for a more carefully painted oil portrait with the transitions made much more subtle in the final layers of paint.
The following illustrations were sketched out in gouache rather than oils but the same principles apply. The female head is painted somewhat lighter than the above head of a male. Notice that the jaw area, although neutralized, is not so greyed-down that it appears that she has a beard. The ears are redder than the cheeks, as is the nose. Note too that the upper lip is usually darker than the lower lip because it casts a shadow while the lower lip catches the light.
By mixing a burnt umber and burnt sienna in zinc white we can create a good mass tone for painting brown skin. The darker the skin, the higher the contrast with the highlights. A small amount of cerulean blue added to the highlights will make them more convincing.
Replacing burnt sienna in the previous mass tone with yellow ochre will give you a good mass tone for many Asian skin tones. A little viridian may be added to the yellow ochre. Notice how both the brown and Asian flesh tones show less differentiation between the forehead, cheek and jaw areas than we saw in the Caucasian flesh tone schema.
The whites of the eyes are never white. Also, you usually have four white areas to contend with, each of them is different. Look closely at this example and you'll see that no two white areas are the same shade of grey. Mix a different tone for each of them.
Some passages and illustrations have been taken from Gouache For Illustration by Rob Howard - Watson Guptill NY